The present invention relates to a fluidic valve device and, more particularly, to a valve assembly which is actuated by a relatively low energy signal, but may nonetheless be employed effectively in systems encountering either flow rates or pressures which are variable.
A "high gain" control valve refers to a valve which is actuated by a low energy signal to control a relatively high flow or pressure. There are many potential applications for control valves responsive to low energy signals. For example, a small control valve is needed for on demand, spot cooling of electronic circuits. The signal might be a process temperature signal in the form of an amplified thermocouple, thermopile or thermister voltage, or a displacement from a thermo-mechanical (thermostatic) sensor, or from signals indicating heat producing circuit activity in the area to be cooled by the control valve. If the control valve is sufficiently small and lightweight it might even be located in the circuit board, very close to the area to be temperature controlled. It would open to deliver cooling fluid directly to an area in response to such a signal and then close in the absence of the signal.
A small, high gain control valve is also needed as a fluid amplifier in fluid control systems. In fluid logic circuits, for example, the ability of one control valve (air relay) to control many others is referred to as "fan out." For example, if the output from one control valve can be used to control eight others, then the fan out is eight. Generally, the higher the fan out, the easier and more economical it is to design complex fluid logic circuits, provided the higher fan out does not come at the price of increased sensitivity to disturbance signals, including vibration, signal noise, or instability due to signal transmission limitations.
Another application for such a control valve is in the field of liquid level control in small reservoirs, where space limitations require very small displacement floats to sense liquid level and operate the refill control valve. The problem is that small displacement results in a low force level available to operate the control valve. Available float valves use some means to amplify the displacement force to a usable level. An example of this application is in single point watering (SPW) systems for industrial lead-acid batteries. Lead-acid batteries use an electrolyte, which is a solution of sulfuric acid and water. Water is consumed as a normal part of the charge/discharge cycle. The water, which is lost to both evaporation and electrolysis, must be replaced on a regular basis to maintain battery performance. Single point watering systems have become widely used for this purpose. A typical SPW system includes a refill control valve in each battery cell, interconnected by a network of tubing. A coupling attached to the tubing allows a water supply to be connected to feed refill water simultaneously into each cell. Depending on the type of SPW system, the water may be provided at very low pressure, such as from a reservoir mounted a few feet overhead, and referred to as "gravity feed," or from a pressurized supply that may be as high as 40 psi. Some SPW systems are designed to operate only with gravity feed supplies and some operate only with pressurized supplies, such as those disclosed in U.S. Pat. Nos. 4,527,593 and 5,048,557.
There are also several SPW systems which can be supplied with either gravity feed or pressurized water supplies. These systems claim to have the advantage that water flow and pressure are generally not very critical to the performance of their systems. However, this is not the case. In general, the valves in these systems behave differently under different supply pressures. In fact, the shut-off level in these valves (the level of electrolyte in the cell at which the refill valve closes) may vary significantly depending on operating pressure. In some cases, operation at pressure above 25 psi can cause premature shut-off, in which the valve closes before sufficient water is added to the cell to cover the battery plates. Subsequent charge and discharge cycles with exposed (not submerged in electrolyte) battery plates can cause permanent damage to the cell. These variable feed pressure valves all employ floats to sense liquid level and provide sufficient force to close the valve. Some designs use levers, which introduce friction and mechanical complexity, and increase the size of the control valve assembly. Others use a combination of stems, arms and links to allow the float to move the valve member into the fluid flow path so that it is swept into a closed position by the drag of the flow. These control valves are designed to close with the flow, so that as supply pressure increases, the required displacement force provided by the float needed to move the valve into a closed position decreases. This accounts for the fact that the liquid level shut-off point drops as supply pressure increases, since less displacement force is needed for shut-off. This variation can lead to problems in service. If the liquid level shut-off point in a battery is set sufficiently high so that high pressure water supplies can be used, then the shut-off level may rise too high if a low pressure supply is later used to top off the battery. If the shut-off level is too high, acid bubbles out of the vent ports during charge. This can seriously damage battery and battery room equipment. Water supply pressure can vary widely depending on many factors, such as the condition of filters, building demand variations, or in some cases portable water supplies used for refilling have water pumps powered by batteries and can lose pressure due to low battery voltage. Also, industrial batteries come in many sizes and capacities. When a battery is on charge, gas bubbles can form which cause the electrolyte to expand. On large, high capacity batteries, there is often very little clearance above the battery plates and the vent opening, so electrolyte is expelled during charging if the level is too high at the start of charge. The optimum shut-off level may be the same for two batteries, but due to expansion of the electrolyte during the charge cycle, the larger battery may not tolerate an increase in shut-off level as occurs under reduced operating pressure. This expansion can exceed the available clearance. These problems are a direct result of the design of the control valve used in float operated valves.
Conventional float operated valves used in single point watering systems are designed to be actuated with relatively small displacement floats. In order for the valve to operate over a wide range of supply pressure (gravity feed to 40 psi pressure) the displacement force must be amplified. This is typically done with lever arms, gears, hinges, pivots and links. A common characteristic of all known SPW float valves designed for operation over a wide pressure range is that the displacement force vector does not act through the center of the valve. The displacement force vector acts at a distance from the valve through a hinged link. This leads to friction and the increased sensitivity of the valve to wear and contaminants, which can interfere with the normal operation of the valve, particularly in the hostile conditions inside a battery cell, where high temperature, mechanical vibration, corrosive acid and floating debris are the norm.
Therefore, a need exists for a control valve which can be operated with a low energy level signal, is not sensitive to operating pressure variations, has accurate shut-off level and is reliable in hostile working conditions. The valve design should be scalable to meet a wide range of physical size and flow capacity requirements. To be practical for most applications it must be very economical to manufacture in high volumes. It would have the actuation force vector generated by the displacement of the float pass through the center of the valve port(s) and therefore operate without levers, arms, links, hinges, pivots or sliding of close fitting parts. This would allow the most compact design envelope and minimize the deleterious effect of friction on the operation and reliability of the valve.